The invention relates to a diplexer for a reflector antenna for transmitting microwave signals. The invention furthermore relates to a method for processing a received signal stored that has been fed into a diplexer.
Due to their very narrow radiation pattern, large reflector antennas require very precise alignment relative to a transmitter and/or receiver, more generally, to a remote station. A beacon signal emitted by the remote station is typically used for alignment. An antenna diagram with a null in the main beam direction is required to allow the beacon signal to be evaluated by the reflector antenna, or by an evaluation unit coupled to the reflector antenna. Whenever the beacon signal deviates from the main beam direction, an additional signal is received that can be used to correct the deviation in direction. The transmission, separation, and evaluation of the beacon signal are effected in addition to the transmission of the actual communication signal. In doing so, the beacon signal must not affect the actual communication signal.
A reflector antenna for transmitting microwave signals typically comprises a diplexer that has a common signal waveguide to transmit a transmit signal and a receive signal. The common signal waveguide comprises a first end and a second end. A horn is connected to the first end of the common signal waveguide, through which a coupling out of the transmit signal and a coupling in of the transmit signal from/into the common signal waveguide are effected. Generally, a plurality of waveguide ports are coupled to the common signal waveguide for the purpose of feeding in the transmit signal into the diplexer and to couple out the receive signal from the diplexer into a receiver network. The waveguide ports are, e.g., distributed symmetrically along the outside of the common signal waveguide, each being in communicative connection with the common signal waveguide.
The particular function of the diplexer is to process a mode mixture of modes from the receive signal in such a way that a differentiation is possible between the actual communication signal and the correction data for the communication signal. At the same time, the diplexer must correctly transmit a transmit signal fed into the plurality of signal waveguides to be coupled out through the horn. Until now, the existing conflict of objectives here has not been satisfactorily solved whereby both of the receive signals must be correctly divided in terms of its communication signal and the correction information, while the transmit signal must be coupled out with the desired polarization from the reflector antenna.
U.S. Pat. No. 3,922,621 discloses a coaxial diplexer for a reflector antenna for the purpose of transmitting microwave signals. The diplexer comprises a first circular waveguide in which a first signal can propagate. It also comprises a second circular waveguide in which a second signal can propagate that is of lower frequency than the first signal, the second waveguide surrounding the first waveguide. One section of the second waveguide is designed as a corrugated waveguide that has a plurality of annular corrugations extending circumferentially in annular fashion. This effectively decouples the transmit signal and receive signal. However, with the diplexer of U.S. Pat. No. 3,922,621 no propagation of a tracking signal is possible by which a correction of the directional deviation of the reflector antenna is able to be determined.
A non-published German patent application DE 10 2008 004 895.8 reveals a signal junction comprising a signal waveguide for the transmission of a transmit signal and a receive signal. A plurality of transmit signal waveguides are provided to feed in the transmit signal, where the signal waveguides are symmetrically arranged along the outside of the common signal waveguide and are in communicative connection with the common signal waveguide. Similarly, a plurality of receive signal waveguides are provided to transmit the receive signal, where the receive signal waveguide is symmetrically connected to the common signal conductor and is also in communicative connection with the common signal waveguide. Incorporation of filters in the receive signal waveguide is required in order to be able to acquire a tracking signal.
U.S. Pat. No. 6,937,202 B2 discloses an approach whereby modes are separated by reducing the horn diameter below a critical diameter. This is called a virtual short circuit. It is not possible to effect a common coupling out of receive signal (from the point of view of the satellite) and tracking signal along with simultaneously isolating the transmit signal. In order to do this, filters are required in the side arms.
U.S. Patent Application Publication No. 2003/0222733 A1 discloses the separation of modes by reducing the horn diameter below the critical diameter using a virtual short circuit. It is not possible to effect a common coupling out of receive signal (from the point of view of the satellite) and tracking signal along with simultaneously isolating the transmit signal. The disclosure relates to ground station applications where the provided structure of the feed system can be used due to the reversed assignment of transmit and receive bands. Filters are absolutely essential in the side arms.
Exemplary embodiments of the present invention provide a diplexer for a reflector antenna that transmits microwave signals, the diplexer providing improved correction of the directional deviation of the reflector antenna. Exemplary embodiments of the present invention also provide a method for processing a receive signal fed into a diplexer, the method providing improved precision in correcting the directional deviation.
Exemplary embodiments of the invention provide a diplexer for a reflector antenna for transmitting microwave signals. The diplexer comprises a common circular signal waveguide to transmit the transmit signal and a receive signal, wherein the diplexer comprises a first end and a second end, wherein a common port is provided at the first end. The diplexer furthermore comprises a waveguide arrangement that is coaxially disposed in the region of a second end of the signal waveguide. In addition, a cylindrical coupler section is provided that is disposed between the first and second ends of the signal waveguide, and connects the waveguide arrangement to the common signal waveguide. The invention is distinguished by the fact that the waveguide arrangement comprises a first circular waveguide and a second circular waveguide so as to create a first and second coaxial waveguide port. When the diplexer is operating, a first signal can propagate within the first circular waveguide, an inner conductor being disposed inside the first waveguide. A receive signal (subsequently also identified as a receive band) is conducted through the first circular waveguide. When the diplexer is operating, a second signal (transmit signal or transmit band) at a lower frequency than the first signal can propagate within a second circular waveguide, the second waveguide surrounding the first waveguide.
The invention furthermore provides a method for processing a signal fed into a diplexer provided according to the invention. In the method according to the invention, a TE11 mode is fed into the common port. A TM11 mode is excited in the signal waveguide and is superimposed with the TE11 mode in such a way that the total energy of the second signal (in the transmit band) flows into the second outer waveguide due to a constructive interference of outer field components and a destructive interference of inner field components, and that the total energy of the first signal (in the receive band) flows into the first inner waveguide due to a constructive of inner field components and a destructive interference of outer field components. When the first TM01 mode is fed in at the common port, the first signal (in the receive band) is converted into the TEM mode of the first waveguide. From the TE11 mode and the TM01 mode of the first signal (in the receive band), information is obtained by processing the modes for the purpose of aligning the reflector antenna.
The invention thus provides an approach where the transmit signal and the receive signal are separated, while simultaneously a transformation of the TM01 mode into the TEM mode is effected, thereby providing a tracking signal in the receive band for antenna alignment in addition to the communication signal. This is made possible by the use of an inner conductor that is disposed inside the first waveguide.
One advantage of this procedure is that the sum and difference signals required for tracking are coupled out under the same conditions, in particular, at the same temperature. This prevents phase errors caused by varying temperatures in the HF paths.
Another advantage is that the tracking signal is coupled out after the transmit signal and receive signal have been separated. As a result, disturbances of the transmit signal by a tracking mode coupler are prevented.
In contrast to the solutions known from prior art, no filters are required in the side arms to isolate the transmit signal. As a result, the feed system is essentially insensitive to uncertainties in manufacture.
The diplexer according to the invention is advantageously a coaxial diplexer. This results from the coaxial arrangement of the first circular waveguide that is surrounded by a second circular waveguide.
It is furthermore advantageous if the inner conductor is pin-shaped. The first waveguide and the inner conductor, in particular, terminate at the same or different levels.
Provision is made in another embodiment whereby the coupler section is designed as the first corrugated waveguide that includes a plurality of corrugations facing towards the inside of the signal waveguide that extend along an inner circumference. The first corrugated waveguide here adjoins the second end of the signal waveguide.
Provision is furthermore made whereby at least a certain segment of the second waveguide is designed as a corrugated waveguide that includes a plurality of corrugations facing towards the inside of the signal waveguide that extend along an inner circumference. The second corrugated waveguide preferably adjoins the coupler section or the second end of the signal waveguide.
Each of the corrugations of the first and/or the second corrugated waveguide are arranged so as to be equidistant from each other. In one specific embodiment, provision can be made whereby the spacing between respective corrugations of the first corrugated waveguide is different from the spacing of the respective corrugations of the second signal waveguide.
The diplexer according to the invention is furthermore distinguished by the fact that the second port (in the sideband) is coupled to a turnstile junction and to two 180° hybrid couplers, or to two coaxial side arm orthomode transducers, in order to generate dual linearly polarized signals. Alternatively, the second waveguide port (in the transmit band) is coupled to a polarizer, a turnstile junction, and two 180° hybrid couplers, or a turnstile junction, two 180° hybrid couplers, and a 90° hybrid coupler, in order to generate dual circular polarization.
In another embodiment, the first waveguide port (in the receive band) is coupled to a turnstile junction and three 180° hybrid couplers in order to generate linear polarization. Alternatively, the first waveguide port (in the receive band) is coupled to a turnstile junction, three 180° hybrid couplers, and a 90° hybrid coupler in order to generate circular polarization.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.